Musical instrument electronic tone processing system



United States Patent Inventor David Bung" 3,476,863 11/1969 Campbell84/1 .01

Cincinnati, Ohio [21] APPL 751,441 Pnmary ExammerWarren E. Ray [22]Filed Aug- 9, 1968 Assistant Examiner-Stanley J. Witkowski [45] PatentedOct 27 1970 Att0meysW. H. Breunig and Hurvitz and Rose and Greene [73]Assignee D. H. Baldwin Company gg r a gz q ABSTRACT: An audio tone froma musical instrument is aprpo plied to a phase splitter to provide twooppositely-phased tone signals, each of which is passed to a respectivefield effect [54] MUSICAL INSTRUMENT ELECTRONIC TONE transistortransmission gate. In addition, the audio tone is con- PROCESSNG SYSTEMverted to a square wave having the same frequency as the fun- 13 Claims,3 Drawing Figg damental frequency of the tone. The square wave is passedto a frequency divider which provides a pair of gating signals for [52]US. Cl 84/1.11, the respective transmission gates the gating Signalsbeing 84/ positely-phased and at half the fundamental frequency of the[51] Int. Cl G10h 1/06, ma The oppositely phased tone signals arealternately Gloh 3/00 passed by the gates and combined in a tone colorfilter circuit [50] FIG! of Search 84/1 .01 which imparts Specifiedmusical tone qualities to h bined signal. in addition, the original tonemay be gated via a further field effect transistor gate by a signalhaving a frequen- [56] References Cmd cy which is one-quarter of thetone fundamental frequency, UNITED STATES PATENTS the gated signal beingpassed to an appropriate tone color 2,514,490 7/1950 H3116" filter. Theoriginal tone is also passed directly to a tone color 2,561,349 /1 arp84/ 1.14 filter. All of the filtered signals are then amplified andpassed 3,006,223 10/1961 Whilem l to a loudspeaker system to provide anacoustic signal of sub- 3,213,l80 10/1965 k r y et aL stantially greatertonal complexity than the original tone and 3,429,976 2/1969 Tomcik8411.12 which is controlled in frequency and amplitude by the 3,440,3251 hwar z et a] 84/ l .25 frequency and amplitude respectively in theinput tone.

n l3 l5 l7 l9 Aumo A DIODE B Q D men-r wave F/F +2 33 TRANS. SHRPER EAUDlO 2| 1 F AMP GATE PHASE AMP L sPL ITTER H GATE 3s 25 I' J HRRRY 0FAMP P TONE COLOR 29 I L f M F l LTERS I GATE 3,7

Patented Oct. 27, 1970 Sheet of 2 AUD|O INPUT TRANS.

DIODE WAVE SHRPER 233 "v G -emE SPLITTER PHASE M v we 37' AMP QRRRY 0FTONE COLOR FILTERS AUDIO' AMP lLJLJ-L l 'r-ll DAV IN VENT OR- BUNGERATTORNEYS MUSICAL INSTRUMENT ELECTRONIC TONE PROCESSING SYSTEMBACKGROUND OF THE INVENTION The present invention relates to tonegeneration systems and more particularly to electronic systems whichrespond to acoustic tones from conventional musical instruments toprovide signals of complex tonal quality.

The concept of electronically processing tones provided by conventionalelectric or nonelectrical musical instruments is known in the prior art.Examples of prior art approaches to such processing may be found in thefollowing US. Pats: Earp, No. 2,561,349; White, No. 3,006,228; Hanert,No. 2,514,490; and Cookerly et al. No. 3,2l3,l80. My copending US. Pat.application, Ser. No. 712,117, filed Mar. 11, 1968 and entitled TONEPROCESSING SYSTEM discloses yet another approach to electronicprocessing of tones provided by conventional musical instruments. Asdiscussed in said application, prior art systems lack a suitable devicefor assuring that the fundamental frequency of a complex musical tonewill, for all frequencies and waveshapes, assume reliable control overthe system. It is desirable, for example, that the simulated voices,electronically produced by the processing system in response to theinput tone, have a signal level which follows changes in the input tonesignal level as closely as possible. In addition, attack anddecay'characteristics of the artificial voices should be as realistic aspossible, and this requires faster response to input tone level changesthan was achievable in the prior art. Moreover, if the harmonic contentof the input waveform for the input tone is changed, for example, byoverblowing a clarinet, a corresponding tone color change should occurin the simulated voices.

My above referenced US. Pat. application discloses a system in whichthese characteristics are considered. More particularly, my prior systemprovides for conversion of the input tone to square waves having thefrequency of the input tone fundamental frequency. The square wave isthen distributed to frequency division and multiplication circuitry toprovide signals corresponding to the various desired simulated voices.The different voice signals are then passed to respective tone colorfilter networks, combined, and then passed to a diode voltage controlledexpression circuit which is responsive to level changes in the inputtone to vary the level and expression characteristics of theartificially generated voice signals. The present invention is concernedwith the same problem as was my prior system; however, the system of thepresent invention represents a significant improvement in providinggreater control over signal level and expression of the simulated voicesby the input tone that was achievable in prior art systems.

It is therefore an object of the present invention to provide anelectronic processing system for input tones, no matter how generated,in which complex output tones are produced at frequencies and amplitudeswhich are controlled directly by the frequency and amplitude of theinput tone.

It is another object of the present invention to provide a toneprocessing system of the type referred to above wherein output toneexpression follows input tone variations more closely than in prior arttone processing systems.

SUMMARY OF THE INVENTION In accordance with the principles of thepresent invention, the input tone signal itself, rather than squarewaves derived therefrom, is passed to the tone color filtering networkvia field effect transistor transmission gates which are operated atfrequencies corresponding toil-re desired simulated voices to beelectronically produced. One set of voice signals is produced byapplying the input tone signal to a phase splitter which in turn appliesa pair of oppositely-phased output signals to a respective pair of fieldeffect transistor gates. The gating signals for controlling transmissionthrough the gates are derived from the input tone signal by means of apulse converter, which converts the input tone signal to a train ofpulses having a frequency equal to the fundamental frequency of theinput tone signal, and a frequency divider which divides the pulse trainfrequency in half to produce two oppositely-phased gating signals eachhaving a frequency equal to half the fundamental frequency of the inputtone signal. Opposite phasing of the gating signal provides alternateoperation of the two field effect transistor gates, the output signalsfrom which are combined to provide a harmonically rich simulated voicesignal at a frequency equal to one half the fundamental frequency of theinput tone signal.

The input tone signal is also applied to an amplifier which applies theamplified version of the input tone signal to a further field effecttransistor gate. The further gate is controlled by a gating signalhaving ,a frequency equal to onequarter of the fundamental frequency ofthe input tone signal, this latter gating signal being derived fromfurther frequency division of the pulse train derived from the inputtone signal. The signal thus passed by the further transmission gate hasa frequency equal to one-quarter of the fundamental frequency of theinput tone signal and thereby represents another simulated voiceproduced electronically by the tone processing system of the presentinvention. The artificially generated voices, as well as the inputsignal itself are applied to an array of tone color filters whichimparts desired musical characteristics and tonal qualities to theindividual voices and in turn applied the resultant signals to anamplifier and loudspeaker system.

By utilizing the input tone signal itself, rather than square wavesderived therefrom, to provide the basis of the individual simulatedvoices, the system provides a complex tonal output having a signal leveland tonal expression which accurately follows the input tone signallevel. In addition, the use of field effect transistorsfor transnn'ssiongates permits one to take advantage of the relatively noise-freecharacteristics of such transistors, whereby substantially no undesiredfrequency components are introduced in the simulated voice signals.Further, by alternately gating the oppositely-phased output signals fromthe phase splitter with correspondingly oppositelyphased gating signalshaving frequencies equal to one-half the fundamental frequency. of thetone, a desirable wave form is obtained for producing realistic sound inthe divide-bytwo voices. More specifically, the combined portions of thegated phase splitter output signals tend to approximate, while notcorresponding precisely to, a square wave having a frequency equal toone-half the input tone fundamental frequency. This type of wave formallows one to obtain very realistic bass clarinet and bassoon tones.

BRIEF DESCRIPTION OF THE DRAWINGS The above and still further objects,features and advantages of the present invention will become apparentupon consideration of the following detailed description of one specificembodiment thereof, especially when taken in conjunction with theaccompanying drawings; wherein:

FIG. 1 is a block diagram of a system according to the presentinvention;

FIGS. 2A through 2M are plots of wave shapes of signals appearing atdesignated points in the system illustrated in FIG. 1;

FIG. 3 is a schematic diagram of a system according to FIG. 1.

DESCRIPTION OF THE-PREP ERRED EMBODIMENT Referring now to FIG. I of theaccompanying drawings an audio input signal A, which may be derived froman accustoelectric transducer 11 operatively associated with a horn,clarinet, guitar, or the like, is applied to a diode waveshaper 13. Byway of example and for facilitating description of system operation, theaudio input signal may take the form of a pure sinusoid such asillustrated in FIG. 2A; however, it is to be understood that the presentsystem is capable of processing input signals of substantially morecomplex waveshapes than a simple sinusoid. Signals appearing atdifierent points in the system of FIG. 1 are designated A through M andare plotted with respect to time in FIG. 2A through 2M respectively.Diode waveshaper 13 converts the input signal to a square wave or plusetrain B as illustrated in FIG. 2B and which has a pulse repetitionfrequency (PRF) equal to the fundamental frequency of the audio inputsignal A. Pulse train output signal B drives a set-reset flip-flop 15which in turn provides a pluse train C having a PRF equal to the audioinput signal fundamental frequency, but a constant amplitude regardlessof amplitude variations in audio input signal A. The wave shape of theoutput signal from flip-flop 15 is illustrated in FIG. 2C. The outputsignal from flip-flop 15 drives two cascaded divide-by-two circuits, 17and 19, respectively. Circuit 17 provides two oppositely-phased squarewave signals, D and E each having a frequency equal to one-half thefundamental frequency of audio input signal A, and which are utilized asgating signals in a manner to be described hereinbelow. Circuit 19provides a square wave signal F which has a frequency equal toone-quarter the fundamental frequency of the audio input signal. SignalsD, E and F are illustrated in FIGS. 2D, 25 and 2F, respectively, of theaccompanying drawings.

Audio input signal A is also applied to a phase splitter network 21which provides two oppositely-phased signals G and a H of substantiallyequal amplitude and having a frequency equal to the fundamentalfrequency of input signal A. Signals G and H are illustrated in FIGS. 2Gand 2H respectively of the accompanying drawings. Signal G, which isopposite in phase to signal A, is applied to the input terminal ofsignal transmission gate 23 and signal I-I, cophasal with signal A, isapplied to the input terminal of signal transmission gate 25. Gate 23also receives signal D at its gate terminal and gate 25 also receivessignal E at its gate terminal. Each of gates 23 and 25 operate to passsignals applied to their input terminals in response to gating signalsbelow a predetermined level at their gate terminals, and to blockpassage of signals applied to their input terminals in response toapplication of a signal above the predetermined signal level at theirgate terminals. Gates which block signal transmission for low levelgating signals and pass signals in response to high level gating signalsmay also be employed within the scope of the present invention. Thesignal passed by gate 23 in response to the gating action of signal D isdesignated as signal I and comprises alternate cycles of signal G. Thesignal passed by gate 25 in response to gating signal E is designated assignal 1 and comprises alternate cycles of signal H. Signals I and l arecombined and applied to an amplifier 27 which provides an amplifiedversion of the combined signals I and J designated as signal K. Theefiect of utilizing oppositely-phased gating signals D and E to gaterespective oppositelyphased input signals G and H is to produce insignal K (see FIG. 2K) a signal corresponding to signal A but in whichalternate cycles are phase-inverted by l80. Where signal A is asinusoid, signal K appears as a pair of adjacent negative half-cyclesfollowed by a pair of adjacent and positive half-cycles, in iterativefashion. As indicated by the dotted line in FIG. 2K, signal K may thusbe looked upon as a harmonically rich approximation of a square wavehaving a frequency equal to one-half the fundamental frequency of theaudio input signal to the system. Where signal A is not a pure sinusoid,signal K is varied somewhat but remains a harmonically rich signal athalf the fundamental frequency of signal A. Signal K comprises thedivide-by-two voice derived by the tone processing system of the presentinvention and is applied to an array of tone color filters, selectableby operation of individual tabs, not illustrated. The tone color filterspermit selective modification of the tone color of the signals appliedthereto so as to produce as closely as possible the tones representingthose of for example, the clarinet, oboe, flute, tuba, saxophone, ordulciana. The output signal from the array of tone color filters isapplied to an audio amplifier 31, which in turn drives a loudspeaker 33.

The audio input signal A is also applied to amplifier 35, whichintroduces a 180? phase shift in the amplified signal L. A portion ofsignal L is applied directly to a section of the voice of the system.Another portion of signal L is applied to the input terminal of atransmission gate 37 which also receives at its gate terminal signal Fprovided by frequency divider circuit 19. Gate 37, like gates 23 and 25,passes signals from its input to its output terminals in response togate signals below a predetermined level and blocks transmission ofsignals between its input and output terminals in response to gatesignals above the predetermined level. The output signal from gate 37 isdesignated as signal M in FIG. 2M. Signal M is a chopped version ofsignal L, having a fundamental frequency equal to one-quarter of thefrequency of the audio input signal to the system due to the fact thatthe frequency of gating signal F is one-quarter of said fundamentalfrequency. Signal M is applied to a further section of the array of tonecolor filters 29 and comprises the basis of the divide-by-four voice sinal.

Referring now specifially to FIG. 3 of the accompanying diawings theaudio input signal received from transducer 11 is applied via couplingcapacitor 41 and base current limiting resister 43 to the base of NPNtransistor T1 connected to one end of a load resistor 45, the other endof which is connected to a +22v. DC supply. A voltage divider comprisingresistors 47 and 49 is connected between the collector of transistor T1and ground, and serves to bias the base of transistor T1 A capacitor 51is connected between the base and collector of transistor T1 andprovides frequency selective feedback to ac centuate response oftransistor T1 as an inverse function of frequency; that is, capacitor 51provides rolloff which accentuates the fundamental frequency of acomplex wave at the expense of the higher harmonics.

The amplified audio signal appearing at the collector of transistor T1is superposed on a DC voltage of about l2v. representing the DC supplyvoltage of 22v. less the DC voltage drop across resistor 45. To thecollector of the transistor T1 are directly connected the cathode ofdiode D1 and the anode of diode D2. A DC path exists through diodes D1and D2 from the 22v. supply to ground through resistor 53 connectedbetween the 22v. supply and the anode of diode D1 and resistor 55connected between the cathode of diode D2 and ground. Nearly one-half ofthe available supply voltage IS dropped across resistor 53, implyingthat the anode of diode D1 is at about 12v. and that both diodes arebiased slightly conductive. When the audio signal goes positive itcharges a capacitor 57 which is connected to the cathode of diode D2 atone end and to ground through resistor 59 at its other end. When theaudio signal goes negative it charges capacitor 61 which is connected atone end to the anode of diode D1 and at its other end to ground throughresistor 59. The audio signal when going positive, for example, chargescapacitor 57 to approximately the peak level of the signal, and thischarge is retained during a half cycle of the audio wave, so that if thepositive half cycle is quite complex, as is usually the case. any dipsof level in the course of the positive half cycle do not affect theoutput level at the base of transistor T2 to which the high voltage sideof resistor 59 is connected. Similarly, when the audio signal goesnegative with respect to the normal DC level at the collector oftransistor T1, diode D1 charges capacitor 61 and prevents transientvoltage drops during the next half cycle from generating reverse currentflows through capacitor 61. Charging of capacitor 61 induces dischargeof capacitor 57 and vice versa. Since transfer of the charging functionbetween capacitors occurs as the input signal wave passes through zerolevel, the system can respond to AC waves over a wide range offi'equencies, on the order of 50 Hz to 5,000 Hz. The double diode,double capacitor detection system, as first disclosed in myabove-referenced US. Pat. application Ser. No. 712,117, may bedenominated a push-pull peak detector, since it responds to alternatepolarities of a wave to provide a clipped AC output signal whichapproximates a-square wave. The closeness of the approximation depends,however, on the complexity of the input wave form; that is, the relativeamplitudes and phases of its component array of tone color filters 29 tocomprise the divide-by-one" partials.

between the collector of transistor T2 and the base of transistor T2,and resistor 59-is connected between the base of transistor T2 andground. Transistor T2 saturates upon sufficiently large positive signalsoccurring at its base, its output having values extending from zero to22v. as the input AC waveform altemates,'and it is designed to saturateon any expected level of output from transducer '11. The output oftransistor T2 is therefore'the square wave designated as signal B inFIG. 1 and illustrated in FIG. 2B.

The output signal from transistor T2 is AC coupled to set-resetflip-flop which operates at the'frequency of the input wave andcomprises two cross connected NPN transistors T3 and T4 in aconfiguration which is conventional and hence is not described in detailherein. The output of flip-flop 15 is applied to cascaded flip-fiops l7and l9,-each substantially identical to flip-flop l5, and arranged tooperate as frequency dividers. Flip-flop 1 7provides signals D and E andflip-flop 19 provides signal F.

The audio input signal A is. also applied via a-coupling capacitor andbase current limiting resistor to the base of NPN transistor T5 whichcomprises amplifier 35 of FIG. 1. Transistor T5 is biased and loaded ina manner substantially similar to transistor T1 and provides at itscollector-an amplified, phase-inverted version of the audio input signalA. This amplified signal is coupled via an AC coupling capacitor to oneend of a variable resistor R1 which has its slider arm connected to thedivide-by-one" voice filtering section of the array of tone colorfilters 29 so that resistor R1 provides selective adjustment of thedivide-by-one voice level.

The amplified audio signal appearing acrossresistor R1 is applied to thebase of NPN transistor T8 connected in emitterfollower configuration.The output signal appearing at the emitter of transistor T8 is ACcoupled to the drain electrode of a P-channel field effect transistorF3, which corresponds to signal transmission gate 37' of FIG. 1.'Thesource electrode of field effect transistor (F ET) F3 is AC coupled to avariable resistor R3, having one end connected to ground'and having itsslider arm connected to the divide-by-four" voice filtering section ofthe array of tone color filters 29. The gate electrode of FET F3receives signal F from flip-flop 19.

The operation of FET F3 is as follows? When the gate electrode isreferenced to a positive DC voltage higher than the pinch off voltage ofthe FET, the FET is off; that is; when the gate electrode is reversebiased there exists a relatively high impedance between the drain andsource electrodes so that no signal is passed therebetween. When thegate electrode is grounded, the FET F3 is on and a very lowimpedanceexists between the drain' and source electrodes,-and therefore a signalapplied to the drain electrode is readily passed to the sourceelectrode. Passage of a signal between the drain and source electrodesis accomplished with minimal attenuation, and the output signal from theFET is ata levelwhich tracks the amplitude of the input signal theretoquite closely. The waveforms of the signals L, F and Mappearing at thedrain, gate and source electrodes respectively have been" described indetail in reference to FIG. 1 above and are illustrated in FIGS. 2L, 2Fand 2M respectively.

Audio input signal A is also applied via a suitable AC couplingcapacitor and base current limiting resistor to the base of NPNtransistor T6, which is connected in phase splitter configuration. Moreparticularly, the base of transistor T6 is biased by a voltagedivider'network comprising a resistor 71 connected between a 22v. DCvoltage source and the base of transistor T6, and resistor 73 connectedbetween the base of transistor T6 and ground. A resistor is connectedbetween the collector of transistor T6 and the 22v. source, and aresistor 77 is connected between the emitter of transistor T6 andground. Resistors 75 and 77 are of equal value so that the signalsprovided at-the-collector and emitter respectively of transistor T6 areof substantially equal amplitude. However, the signal appearing at thecollector of transistor T6 is a phase-inverted function of the AC signalapplied to the base of transistor'T6,-whereas the signal appearing atthe-emitterelectrodeof transistor T6 is not phase-inverted.

This'phase-splittingaction of transistor T6 provides oppositely-phasedsignals having frequencies which are equal to the frequency of audioinput signal A and having amplitudes which closely track the-amplitudeofinputsignal A. The collector of transistor" T6 is AC coupledto thedrainelectrode of field effect transistor F1 comprising gate 23 .ofFIG. 1. Similarly the emitter electrode of transistor T6 is AC coupledto the drain electrode of field effect transistor F2 comprising gate25'o'f FIG. 1. Field effect transistors F1 and F2 receive signals 'D andE "respectivelyat their'gate electrodes, and 0' rate in amanner assubstantially described for transistor F above. Thus signal G appearingat the collector of transistor T6 is selectively gated'through FET Fl bysignal D to provide signal I, whereas signal H appearing at the emitterelectrode of-transistor T6 is selectively gated through FET F2 by signalE to provide signal .I. Signalsl and J are combined and applied acrossvariable resistor R2 to ground, the. center arm of which is AC coupledto the base of NPN transistor T7. Transistor T7 is connectedinconventional class A amplifier configuration and provides signal K tothe divide-by-two" section of the array of tone color filters 29. Thesignal level of the "divide-by-two voice signal is selectivelyadjustable by means of R2.

The output signals from the array of tone color filters 29 are combinedand applied to audio amplifier 31 and intum to loudspeaker 33 asdescribed above in relation to FIG. I.

In summary the various individual voices artificially obtained by thesystem of the present invention are produced as follows:

The"divide-by-one voice signals are obtained by amplifying the originalaudio input signal A by means of amplifier 35 and applyingthe resultingwave form to the respective di- 'virie-by-one voice filtering section ofthe array 29;

The *divide-by-two" voices are obtained by feeding the original audioinput signal A to phase splitter 21, the opposite ly-phased output ofwhich are selectively gated by oppositelyphased gating signals atone-half the fundamental frequency of the audio signal, the gatedsignals being combined and applied to the divide-by-two voice'filteringsections of array 29;

The *divide-by-four' voice signals are obtained by gating audio signal Aby a signal corresponding to one-quarter of the frequency of theinputsignal and-applying the resulting gated signal to the'divide-by-four" voice filtering section of array 29.

The reason for employing phase splitter 21 to produce the divide-by-twovoice signals, is that the waveform of signal K is desirable from afiltering standpoint for use in obtaining realistic sounds ofdivide-by-two voices. It can be seen, for

example, that the waveform of signal K tends to approximate, withoutactually corresponding identically to, a square wave with a fundamentalfrequency equal to one-half theinput fundmental frequencyThis type ofwave form has been found to be conducive to readily obtaining arealistic bass clarinet voice.

' Utilization of the FET gates to selectively pass the audio inputsignals at gating frequencies which are submultiples of the fundamental"signal frequencyv provides much more realistic'attack and decaycharacteristics of the various simulated voice'tones than was achievablewith prior art systems. The FET g'atesthemselves are relatively noisefree, and thereforeintroduce substantially no undesired frequencycomponents in the simulated voices of the processing system.. Inaddition; by using the actual input tone for producing the variousvoices, the output is expressed precisely as the input. lfthe harmoniccontent of the input waveform is changed, for example, by overblowingthe instrument providing the input signal, the corresponding tone changeoccurs in the artificial voices with varying degrees. Tonal expressionis achieved with much faster response to input signal level changes thanprior art systems, and the various artificial voices passed through theFET gates are permitted to have level change ranges which correspond tothe range of input signal level.

While I have described and illustrated one specific embodiment of myinvention, it will be clear that variations of the details ofcontruction which are specifically illustrated and described may beresorted to without departing from the true spirit and scope of theinvention as defined in the appended claim.

I claim:

1. In a tone signal processing system for imparting complex tonalqualities to an input tone signal:

pulse converter means responsive to said input tone signal for providinga train of pulses having a fundamental frequency equal to thefundamental frequency of said input tone signal;

phase splitter means responsive to said input tone signal for providinga pair of oppositely-phased signals at the fundamental frequency of saidinput tone signal;

first gating means responsive to a first gating signal for selectivelypassing a first of said pair of oppositely phased signals;

second gating means responsive to a second gating signal for selectivelypassing a second of said pair of oppositely phased signals;

frequency divider means responsive to said train of pulses vforproviding as said first and second gating signals respective first andsecond gating pulse trains of opposite phase and at a frequency equal tothe fundamental frequency of said input tone signal divided by tworaised to a predetermined integer power; and

means for combining the portions of said oppositely-phased signalspassed by said first and second gating means.

2. The system according to claim I further comprising tone color filtermeans connected to said means for combining for musically modifying thecombined portions of said oppositelyphased signals passed by said firstand second gating means.

3. The system according to claim 1 wherein said specified integer powerof two is unity.

4. The system according to claim 1 wherein said first and second gatingmeans each comprises a field effect transistor having source, drain andgate electrodes, said field effect transistors being connected forselectively passing signals between said source and drain electrodes inresponse to application of a gating signal to said gate electrode.

5. The system according to claim 1 further comprising:

third gating means responsive to a third gating signal for selectivelypassing said input tone signal; and

wherein said frequency divider means includes means for providing assaid third gating signal a pulse train having a frequency equal to thefundamental frequency of said input tone signal divided by two raised toa further integer power other than said specified integer power.

6. The system according to claim 5 wherein said specified integer poweris one and said further integer power is two.

7. The system according to claim 6 further comprising tone color filtermeans for musically modifying the combined portions of saidoppositely-phased signals passed by said first and second gating meansand the portion of said input tone signal passed by said third gatingmeans.

8. The system according to claim 7 further comprising additonal tonecolor filter means for musically modifying said input tone signalsindependently of those portions of said input tone signal passed by saidfirst, second and third gating means.

9. The system according to claim 7 wherein said first, second and thirdgating. means each comprises a field effect transistor having drainsource and gate electrodes, each said field effect transistor beingconnected to pass its respective signals between said drain and sourceelectrodes in response to a respective gating signal at said gateelectrode.

10. The system according to claim 9 wherein said pulse generator meanscomprises a push-pull peak rectifier circuit connected to saidtransducer means, said circuit comprising:

a first junction to which said electrical signal is applied;

a first diode having its cathode connected to said first junction;

a first capacitor, one end of which is connected to the anode of saidfirst diode;

a second diode having its anode connected to said first junction;

a second capacitor, one end of which is connected to the cathode of saidsecond diode;

means for connecting the other ends of said first and second capacitorstogether at a second junction;

a load resistor connected between said second junction and ground;

a transistor clipping circuit responsive to the voltage across said loadresistor and arranged to become alternately nonconductive and saturatedas the voltage across said load resistance changes algebraic sign; and

a flip-flop having a single control tenninal responsive to saidtransistor clipping circuit.

11. In a system for processing the variable frequency acoustic tone of anonelectrical musical instrument;

a transducer for coupling said acoustic tone to said system andconverting said tone to an electrical signal having a frequency equal tothe acoustic tone frequency and an amplitude proportional to theacoustic tone amplitude;

gating means responsive to a gating signal for selectively passing saidelectrical signal, said gating means comprising a field effecttransistor having drain, source and gate electrodes, said electricalsignal being selectively passed between said drain and source electrodesin response to application of said gating signal to said gate electrode;

pulse generator means responsive to said electrical signal for providinga train of pulses at a frequency equal to the fundamental frequency ofsaid acoustic tone;

frequency divider means responsive to said train of pulses for providinga further train of pulses having a frequency equal to the frequency ofsaid first mentioned train of pulses divided by some integer power oftwo; and

means for applying said further train of pulses to said gate electrodeas said gating signal.

12. In the system according to claim 11, tone color filter means formusically modifying the electrical signal passed by said gating means.

13. The system according to claim 12 wherein said pulse generator meanscomprises a push-pull peak rectifier circuit connected to saidtransducer means, said circuit comprising:

a first junction to which said electrical signal is applied;

a first diode having its cathode connected to said first junction;

a first capacitor, one end of which is connected to the anode of saidfirst diode;

a second diode having its anode connected to said first junction;

a second capacitor, one end of which is connected to the cathode of saidsecond diode;

means for connecting the other ends of said first and second capacitorstogether at a second junction;

a load resistor connected between said second junction and ground;

a transistor clipping circuit responsive to the voltage across said loadresistor and arranged to become alternately nonconductive and saturatedas the voltage across the load resistance changes algebraic sign; and

a flip-flop having a single control terminal responsive to saidtransistor clipping circuit.

